This invention relates to analyzers for determining the level of a selected chemical in a process fluid.
A typical analyzer for measuring the level of a chemical in a process fluid includes a voltammetric sensor that supports one or more electrodes in electrolytic contact with the fluid. The electrodes are immersed in an electrolytic solution of fixed composition at one end of the sensor and are separated from the process fluid by a membrane that is permeable to the selected chemical. This type of sensor is known as a Clark cell when the chemical to be measured is oxygen or its allotropes such as ozone.
When the sensor is inserted in the process fluid and an oxygen-permeable membrane is used, oxygen in the fluid diffuses through the membrane into the electrolytic solution. As a result, when the electrodes are energized (with either D.C. or pulsed potential) they produce an electrical signal that is proportional to the level of oxygen in the electrolyte, and hence the amount of oxygen in the process fluid.
Such sensors may be adversely affected by membrane breakage or fouling. For example, the membrane may become fouled during use by materials (such as dirt, oil, grease, sludge, etc.) in the process fluid that collect on the membrane, reducing its permeability. As a result, the signal produced by the sensor will no longer accurately reflect the oxygen level in the process fluid, thereby leading to measurement errors. This problem is particularly acute when the process fluid comprises sludge-laden waste water in sewage treatment plants.